Abaddon isn't the beast that was and is not. Abaddon is only used once, and the beast the was and is not is a person possessed by Abaddon or his peers.
Hal, Revelation 17:8 has two parts 17a and 17b.
The beast that John in the first century saw - was and is not. That person lived before John's time, and was dead. His disemboided spirit, can be referred to as an unclean spirit, in the bottomless pit.
a. The beast that thou sawest was, and is not; and shall ascend out of the bottomless pit, and go into perdition:
In part b, is the end times person. That end times person will be possessed by the unclean spirit - transforming the end times person into the beast.
b. and they that dwell on the earth shall wonder, whose names were not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is.
Here's why it is not Abaddon.
In Revelation 13, the false prophet has an image made of the beast - after the beast is mortally wounded and healed (and possessed)... the image is the AOD beginning the great tribulation, and all of the judgements. So the end times person has been killed and come back to life possessed (by Abaddon)?
But wait Abaddon is still in the bottom pit - long after the judgments begin - so it can't be Abaddon.
In order
1. end times person killed and come back to life, possessed - Revelation 13
2. an image of the person, the Abomination of Desolation - Revelation 13
3. the great tribulation begins (Matthew 24:15)
4. the judgements begin, the trumpets,
5. Abaddon released from the bottomless pit, at the fifth trumpet.
So as you can see the person has become the beast (possessed)
before Abaddon is released from the bottomless pit.
